Mailing List that Conceals/Rewrites all E-mail Addresses from the Headers

The spam bombardment is getting out of hand. With this project, we are trying to defend ourselves from the onslaught. (a) I have implemented this feature in the past but don't have the time now. (b) This is based on Open Source software already available (such as postfix/sendmail/mailman), all you will need to do is provide some value added functionality on top of it. The goal is to implement a mailing list with the following requirements: [Read the full description of the project requirements in the attached image] Please provide some level of detail on how you would implement this. If you send a proposal that includes every skill since the computer was invented, your proposal will not be considered. I better see words like "Linux", or "open source" in your resume. Oh, the most I can possibly justify for is about $100. Not much more. The person with the right skillset can do this in 2-4 hours, with plenty coffee breaks.